Fri·Sep 4, 2020Friday·September 4, 2020

1. 01*

   Status of CME Search Before Isobar Collisions and Methods of Blind Analysis From STAR

   Prithwish Tribedy (for the STAR Collaboration)🇺🇸

   The STAR collaboration is currently pursuing the blind analysis of the data for isobar collisions that was performed at RHIC in the year 2018 to make a decisive test of the Chiral Magnetic Effect (CME). Why is it so difficult to detect signals of CME in the experiment? Do we really understand different sources of background? Why observing similar charge separation between p/d+A and A+A does not stop us from pursuing the search for CME? In this contribution, I attempt to address some of these questions and briefly outline a few recent STAR analyses based on new methods and observables to isolate the possible CME-driven signal and non-CME background contributions at the top RHIC energy. Finally, I describe the procedure for the blind analysis of the isobar data. An outstanding question remains -- what happens if we go down in energy? I address this by discussing how the new event-plane detector (EPD) upgrade provides a new capability at STAR towards CME search using the data from the RHIC BES-II program.

   nucl-exhep-phnucl-thJ.Phys.Conf.Ser.(2020)·4 citations
2. 02*

   Centrality determination with a forward detector in the RHIC Beam Energy Scan

   Skipper Kagamaster🇺🇸 · Rosi Reed🇺🇸 · Michael Lisa🇺🇸

   Recently, Chatterjee et al used a hadronic transport model to estimate the resolution with which various experimental quantities select the impact parameter of relativistic heavy ion collisions at collision energies relevant to the Beam Energy Scan (BES) program at the Relativistic Heavy Ion Collider (RHIC). Measures based on particle multiplicity at forward rapidity were found to be significantly worse than those based on midrapidity multiplicity. Using the same model, we show that a slightly more sophisticated measure greatly improves the resolution based on forward rapidity particles; this improvement persists even when the model is filtered through a realistic simulation of a recent upgrade detector to the STAR experiment. These results highlight the importance of optimizing centrality measures based on particles detected at forward rapidity, especially for experimental studies that search for a critical point in the QCD phase diagram. Such measurements usually focus on proton multiplicity fluctuations at midrapidity, hence selecting events based on multiplicity at midrapidity raises the possibility of nontrivial autocorrelations.

   nucl-exPRC(2021)·8 citations
3. 03*

   Search for alpha decay of naturally occurring osmium nuclides accompanied by gamma quanta

   P.Belli🇮🇹 · R.Bernabei🇮🇹 · F.Cappella🇮🇹 · V.Caracciolo🇮🇹 · R.Cerulli🇮🇹 · F.A.Danevich🇺🇦 · A.Incicchitti🇮🇹 · D.V.Kasperovych🇺🇦 · V.V.Kobychev🇺🇦 · G.P.Kovtun🇺🇦 · N.G.Kovtun🇺🇦 · M.Laubenstein🇮🇹 and 5 other authors

   A search for $\alpha$ decay of naturally occurring osmium isotopes to the lowest excited levels of daughter nuclei has been performed by using an ultra-low-background Broad-Energy Germanium $\gamma$-detector with a volume of 112 cm${}^3$ and an ultra-pure osmium sample with a mass of 118 g at the Gran Sasso National Laboratory of the INFN (Italy). The isotopic composition of the osmium sample has been measured with high precision using Negative Thermal Ionisation Mass Spectrometry. After 15851 h of data taking with the $\gamma$-detector no effect has been detected, and lower limits on the $\alpha$ decays were set at level of $\lim T_{1/2}\sim 10^{15}-10^{19}$ yr. The limits for the $\alpha$ decays of ${}^{184}$Os and ${}^{186}$Os to the first excited levels of daughter nuclei, $T_{1/2}{(}^{184}$Os$)\ge 6.8\times 10^{15}$ yr and $T_{1/2}{(}^{186}$Os$)\ge 3.3\times 10^{17}$ yr (at 90% C.L.), exceed the present theoretical estimates of the decays half-lives. For ${}^{189}$Os and ${}^{192}$Os also decays to the ground states of the daughter nuclei were searched for due to the instability of the daughter nuclides relative to $\beta$ decay.

   nucl-exPRC(2020)·17 citations
4. 04*

   Proton spin after 30 years: what we know and what we don't?

   Xiangdong Ji🇺🇸 · Feng Yuan🇺🇸 · Yong Zhao🇺🇸

   More than three decades has passed since the European Muon Collaboration published the first surprising result on the spin structure of the proton. Much theoretical and experimental progress has been made in understanding the origins of the proton spin. In this review, we will discuss what we have learned so far, what are still missing, and what we shall expect to learn from the upcoming experiments including JLab 12 GeV and Electron-Ion Collider. In particular, we focus on first principles calculations and experimental measurements of the total gluon helicity $\Delta G$, and quark and gluon orbital angular momenta.

   ↳ hep-phhep-exhep-latnucl-ex+1Nature Rev.Phys.(2021)·139 citations
5. 05*

   Alternate Solution of the $\alpha$-Potential Mystery

   Vlad Avrigeanu · Marilena Avrigeanu🇷🇴

   A consistent set of statistical-model input parameters, validated by analysis of various independent data, makes possible the assessment of an $\alpha$-particle optical model potential [Phys. Rev. C {\bf 90}, 044612 (2014)] also for nucleon-induced $\alpha$-emission within $A$$\sim$60 mass-number range. The advantage of recent data for low-lying states feeding is taken as well. Consideration of additional reaction channels leading to increase of the $\alpha$-emission beyond the statistical predictions has concerned the pickup direct interaction and Giant Quadrupole Resonance similar features.

   ↳ nucl-thnucl-ex0 citations
6. 06*

   A fast centrality-meter for heavy-ion collisions at the CBM experiment

   Manjunath Omana Kuttan🇩🇪 · Jan Steinheimer🇩🇪 · Kai Zhou🇩🇪 · Andreas Redelbach🇩🇪 · Horst Stoecker🇩🇪

   A new method of event characterization based on Deep Learning is presented. The PointNet models can be used for fast, online event-by-event impact parameter determination at the CBM experiment. For this study, UrQMD and the CBM detector simulation are used to generate Au+Au collision events at 10 AGeV which are then used to train and evaluate PointNet based architectures. The models can be trained on features like the hit position of particles in the CBM detector planes, tracks reconstructed from the hits or combinations thereof. The Deep Learning models reconstruct impact parameters from 2-14 fm with a mean error varying from -0.33 to 0.22 fm. For impact parameters in the range of 5-14 fm, a model which uses the combination of hit and track information of particles has a relative precision of 4-9 % and a mean error of -0.33 to 0.13 fm. In the same range of impact parameters, a model with only track information has a relative precision of 4-10 % and a mean error of -0.18 to 0.22 fm. This new method of event-classification is shown to be more accurate and less model dependent than conventional methods and can utilize the performance boost of modern GPU processor units.

   ↳ hep-phnucl-exnucl-thPLB(2020)·46 citations
7. 07*

   Jet quenching in the hadron gas: An exploratory study

   Hannah Elfner🇩🇪 · Philipp Dorau🇩🇪 · Jean-Bernard Rose🇩🇪 · Daniel Pablos🇳🇴

   In most calculations of hard particle suppression in heavy-ion reactions the hadronic stage has been neglected due to formation time arguments. Most of the hard particle shower exits the hot and dense medium before the system enters the hadronic evolution. In this contribution, a first assessment within the hadronic transport approach SMASH (Simulating Many Accelerated Strongly-interacting Hadrons) of rescattering effects on hard particles is presented. In particular, it is shown that the hadronic energy loss depends on the particle species as well as the energy of the probe. A parametrization for the $⟨\tilde{q}⟩$ parameter as a function of temperature and particle energy is given for pions. Overall, major effects of the hadronic stage are expected in the transverse momentum range from 2-10 GeV and therefore jet sub-structure analysis and (hard-soft) correlation observables might be affected.

   ↳ nucl-thhep-phnucl-exPoS(2021)·2 citations
8. 08*

   Electron capture in stars

   Karlheinz Langanke🇩🇪 · Gabriel Martínez-Pinedo🇩🇪 · Remco Zegers🇺🇸

   Electron captures on nuclei play an essential role for the dynamics of several astrophysical objects. The capture rate can be derived in perturbation theory where allowed nuclear transitions (Gamow-Teller transitions) dominate, except at the higher temperatures achieved in core-collapse supernovae where also forbidden transitions contribute significantly to the rates. There has been decisive progress in recent years in measuring Gamow-Teller (GT) strength distributions using novel experimental techniques based on charge-exchange reactions. These measurements provide not only data for the GT distributions of ground states for many relevant nuclei, but also serve as valuable constraints for nuclear models which are needed to derive the capture rates for the many nuclei, for which no data exist yet. In particular models are needed to evaluate the stellar capture rates at finite temperatures, where the capture can also occur on excited nuclear states. There has also been significant progress in recent years in the modelling of stellar capture rates. This has been made possible by advances in nuclear many-body models as well as in computer soft- and hardware. Specifically to derive reliable capture rates for core-collapse supernovae a dedicated strategy has been developed based on a hierarchy of nuclear models specifically adapted to the abundant nuclei and astrophysically conditions present at the various collapse conditions. This manuscript reviews the experimental and theoretical progress achieved recently in deriving stellar electron capture rates. It also discusses the impact these improved rates have on the various astrophysical objects. (Abridged)

   ↳ nucl-thastro-ph.HEnucl-exRept.Prog.Phys.(2021)·59 citations
9. 09*

   Coulomb sum rule for ${}^4$He and ${}^{16}$O from coupled-cluster theory

   J. E. Sobczyk🇩🇪 · B. Acharya🇩🇪 · S. Bacca🇩🇪 · G. Hagen🇺🇸

   We demonstrate the capability of coupled-cluster theory to compute the Coulomb sum rule for the ${}^4$He and ${}^{16}$O nuclei using interactions from chiral effective field theory. We perform several checks, including a few-body benchmark for ${}^4$He. We provide an analysis of the center-of-mass contaminations, which we are able to safely remove. We then compare with other theoretical results and experimental data available in the literature, obtaining a fair agreement. This is a first and necessary step towards initiating a program for computing neutrino-nucleus interactions from first principles and supporting the experimental long-baseline neutrino program with a state-of-the-art theory that can reach medium-mass nuclei.

   ↳ nucl-thhep-exnucl-exPRC(2020)·19 citations
10. 10*

    Moving away from singly-magic nuclei with Gorkov Green's function theory

    Vittorio Somà🇫🇷 · Carlo Barbieri🇬🇧 · Thomas Duguet🇫🇷 · Petr Navrátil🇨🇦

    Ab initio calculations of bulk nuclear properties (ground-state energies, root mean square charge radii and charge density distributions) are presented for seven complete isotopic chains around calcium, from argon to chromium. Calculations are performed within the Gorkov self-consistent Green's function approach at second order and make use of two state-of-the-art two- plus three-nucleon Hamiltonians, $NN$+$3N\text{(lnl)}$ and NNLO${}_{\text{sat}}$. An overall good agreement with available experimental data is found, in particular for differential energies (charge radii) when the former (latter) interaction is employed. Remarkably, neutron magic numbers $N=28,32,34$ emerge and evolve following experimental trends. In contrast, pairing gaps are systematically underestimated. General features of the isotopic dependence of charge radii are also reproduced, as well as charge density distributions. A deterioration of the theoretical description is observed for certain nuclei and ascribed to the inefficient account of (static) quadrupole correlation in the present many-body truncation scheme. In order to resolve these limitations, we advocate the extension of the formalism towards incorporating breaking of rotational symmetry or, alternatively, performing a stochastic sampling of the self-energy.

    ↳ nucl-thnucl-exEPJA(2021)·42 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.